Review of the animal and clinical pharmacology of diflunisal.

Diflunisal is a new salicylic acid derivative identified after a search for a compound with improved potency, enhanced gastrointestinal tolerance relative to its antiinflammatory activity, and a longer duration of action than that of aspirin. Animal and clinical studies have confirmed these properties. As an inhibitor of cyclooxygenase tested in vitro in a sheep seminal vesicle preparation, diflunisal was less potent than indomethacin but 10 to 20 times more active than aspirin. In addition, it was shown biochemically to act as a moderate free radical scavenger. Diflunisal is well absorbed from the gastrointestinal tract, is subject to dose-dependent pharmacokinetics (like aspirin), and reaches steady-state levels in a predictable fashion in most persons. The drug is excreted by the kidneys, and its apparent half-life is lengthened in the presence of renal failure. A number of drug interactions have been described. Diflunisal produces reversible effects on platelet aggregation when given in high doses, whereas aspirin produces irreversible aggregation at low doses. Measurements of fecal blood loss and endoscopic examinations have confirmed the improved gastrointestinal tolerance of diflunisal compared to aspirin.